In large houses, servants would use these to warm up the beds for their masters and mistresses. Warming pans or bedwarmers were also used. These were large copper pans with a very long handle, filled with hot coals from the fire. The pan was slid under the sheets and moved around constantly to warm up the cold sheets without scorching them. After making everything warm and cosy for her employers, a maid would then often have to sleep in a freezing cold bed.
Image courtesy of Cleveland Ironstone Mining Museum